Same reason you try to save somebody who wants to jump from a bridge? Cost is marginal and potential benefit is huge.

Additionally if it was optional people would forget to do it more often even if they don't consciously choose to risk their lives for no reason.

BTW they are not only endangering themselves - they also endanger their kids.

> Same reason you try to save somebody who wants to jump from a bridge? Cost is marginal and potential benefit is huge.

If it's a considerate decision, I support people's right to ending their own life. Though I grant that jumping off a bridge is inconsiderate.

> BTW they are not only endangering themselves - they also endanger their kids.

So the seatbelt mandate should only apply when kids are in the car, or only to kids?

> If it's a considerate decision, I support people's right to ending their own life.

I support euthanasia after proper waiting period and psych evaluation.

But if I see someone trying to end their life on a street I'm trying to stop them. It's far more likely it's impulsive and not a rational, thought-out decision.

Same with not using seatbelts. There's basically zero reasons not to, so the probability of it being someone exercising their freedoms after a careful consideration is basically zero.

> So the seatbelt mandate should only apply when kids are in the car, or only to kids?

It should apply always, because the benefit is literally life and death, and the cost is basically nothing. Why complicate law, then?

In addition to all the sensible reasons others have pointed out, if you crash at a high enough speed without a seatbelt you become a projectile. If you are in the back seat when this happens, you are most certainly a danger to those in the front seats.

If the seatbelt saves your life from an accident in which you were at fault, it is easier to prosecute and extract compensation from the living than from the dead.

> In addition to all the sensible reasons others have pointed out, if you crash at a high enough speed without a seatbelt you become a projectile.

This pales in comparison to the projectile that your care already is.

In any case, just work out the expected level of danger, convert to monetary units, and tax people who don't wear seatbelts.

> If the seatbelt saves your life from an accident in which you were at fault, it is easier to prosecute and extract compensation from the living than from the dead.

Tax non-seatbelt-wearers ahead of time. Or make sure everyone has insurance, get the money from the insurance, and beancounters at the insurace will make sure premiums go up for non-seatbelt-wearers. (And use the full force of the law against people without insurance. Or have some clever mechanism design, like selling default insurance with petrol, but give people with proven insurance a discount on that, etc.)

> However people who don't want to wear seatbelts generally only endanger themselves.

If they sell the vehicle, the decision was already made for the new owner (nobody would buy separate aftermarket seatbelts for a used car). So no, they also endanger other people. Mandating them outright is the right decision.

No one is forcing you to buy a specific used car.

> (nobody would buy separate aftermarket seatbelts for a used car)

I would assume most people who want seatbelts in the first place would buy a car that comes with seatbelts, even when buying a used car.

> No one is forcing you to buy a specific used car.

In a hypothetical situation with no mandated seatbelts it could take decades for the market of new cars be close to 100% with seatbelts at best. And of course much longer for the used cars market. So yes, many buyers in the meantime would essentially be forced to buy such a car, simply because at their price point and locality there isn't one available with a seatbelt.